1. Field of the Invention
The present invention relates to a method of making a fiber reinforced resin tank structure, and to apparatus especially adapted for use in said method, said method and apparatus being particularly adapted for forming tank structures of varying diameters.
2. Description of the Prior Art
One method of making a fiber reinforced resin tank is disclosed in U.S. Pat. No. 3,524,780, Clements, in which a "birdcage" type knockdown steel framework mandrel is constructed on a glass-resin tank bottom layer. This "birdcage" framework has a plurality of peripheral vertical columns which collectively define a circumference generally corresponding to the configuration of the inner surface of the tank to be formed. Then a plurality of sheets of plywood, fiber board, or the like are mounted to the columns of this framework. Thereafter, the entire framework is rotated, with a glass fiber-resin material being wound helically around the plywood sheets to form the tank structure.
U.S. Pat. No. 3,562,047, Carlini, discloses a method of making a fiber reinforced resin tank in which a mandrel is formed with a plurality of arcuate panels vertically aligned and arranged in a cylindrical configuration. The edges of the panels have inwardly extending flanges, by which the several panel sections are attached to the other. Two adjacent sets of such flanges are angled and make parallel to one another so that after the tank structure is wound on the mandrel, the panel section between such sets of flanges can be removed. This permits the remaining panels of the mandrel to be flexed moderately inwardly to permit the formed tank structure to be moved free of the mandrel and upwardly, so that a subsequent tank section can be made at a location below the upper tank section just formed. Presumably the panels of the mandrel have sufficient rigidity to provide a mandrel having sufficient structural strength to enable the material application to be accomplished without distortion of the mandrel.
U.S. Pat. No. 3,843,429, Jessup, shows yet another method of making a fiber reinforced resin tank structure, wherein there is attached to a plurality of vertical beams a number of arcuate liner panels that actually become part of the tank structure. Resin impregnated fibers are wrapped around these liner panels, with the final structure being a composite of these panels and the resin impregnated fibers.
U.S. Pat. No. 2,669,010, Perkins, shows a method of making cylindrical tank sections wherein a plurality of metal panels, having vertical edge flanges are secured one to another to form the cylindrical tank section. To adjust the curvature of the panels to the desired configuration, prior to joining the panels one to another, a plurality of arcuate stays are inserted in the panel sections. After the panels are joined together, the stays are removed, with the adjoining flange sections of the panels tending to pivot about the points of fastening to form tightly sealed joints of the finished tank structure.
Other patents relating generally to this art are: U.S. Pat. No. 2,579,183, Freyssinet; U.S. Pat. No. 3,700,512, Pearson et al; U.S. Pat. No. 3,783,060, Goldsworthy et al; U.S. Pat. No. 3,794,540, Griffith; and the U.S. Pat. No. 3,822,167, Piola.
One of the critical problems which exists in the prior art is to provide a method and apparatus which is readily adaptable to making tanks of different diameters. One method is simply to provide a number of cylindrical mandrels or forming structures of different diameters, with there being a sufficient number of these to make tanks of the sizes most commonly required. However, with the rather large diameter of tanks invloved (e.g. 20 to 30 feet in diameter or greater), there is a fair capital investment involved in providing even one structure or mandrel of a size sufficient to form such a tank. If a single mandrel or forming structure is used, and it is to be made in such a manner that it can assume cylindrical configurations of different diameters, there is the problem of providing the mandrel or forming structure with sufficient rigidity and structural strength to provide adequate support during the forming process within the tolerances required (which tolerances usually permit the finished structure to be no more than 1% out of round). Finally, to be able to produce such tank structures at a competitive cost, there are important considerations with regard to ease of operation, reliability, durability of the components used, etc. These become especially critical where the tank or tank sections are being made at an "on site" location, rather than at a factory.
Accordingly, it is an object of the present invention to provide a method and apparatus for fabricating fiber reinforced resin tank structures, said method and apparatus being readily adapted for making tank structures of different diameters, and also being readily adapted for use in a factory or at an "on site" location.